Apparatus and method for isolating and measuring movement in metrology apparatus

ABSTRACT

An improved metrology apparatus, such as a scanning probe microscope (SPM), has an actuator that controls motion in three orthogonal directions when it is selectively and electrically stimulated. The X-Y section of the actuator, preferably a piezoelectric actuator, controls motion in the X and Y-directions and the Z-section of the actuator controls motion in the Z-direction. A flexure is attached to the actuator and is mounted on a reference structure to prevent unwanted X and Y-motion by the Z-section of the actuator from moving a probe attached to the flexure. Preferably, two mirrors are mounted on the flexure. In operation of the SPM, a light beam is directed towards these mirrors. When the flexure moves in the Z-direction, one of the mirrors is deflected and causes the reflected light to move across a detector, generating a signal representative of a change in the Z-position of the flexure and the probe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to scanning probe microscopes (SPMs) and otherrelated metrology apparatus. More particularly, it is directed toapparatus and methods for measuring the movement of a probe of, forexample, an SPM, and minimizing the negative effects associated withparasitic movement of such a probe.

2. Discussion of the Prior Art

Scanning probe microscopes are typically used to determine the surfacecharacteristics of a sample, commonly biological or semiconductorsamples, to a high degree of accuracy, down to the Ångstrom scale. Twocommon forms of the scanning probe microscope are shown in FIGS. 1A and1B. A scanning probe microscope operates by scanning a measuring probeassembly having a sharp stylus over a sample surface while measuring oneor more properties of the surface. The examples shown in FIGS. 1A and 1Bare atomic force microscopes (“AFMs”) where a measuring probe assembly12 includes a sharp stylus 14 attached to a flexible cantilever 16.Commonly, an actuator such as a piezoelectric tube (often referred tohereinafter as a “piezo tube”) is used to generate relative motionbetween the measuring probe 12 and the sample surface. A piezoelectrictube is a device that moves in one or more directions when voltages areapplied to electrodes disposed inside and outside the tube (29 in FIG.1C).

In FIG. 1A, measuring probe assembly 12 is attached to a piezoelectrictube actuator 18 so that the probe may be scanned over a sample 20 fixedto a support 22. FIG. 1B shows an alternative embodiment where the probeassembly 12 is held in place and the sample 20, which is coupled to apiezoelectric tube actuator 24, is scanned under it. In both AFMexamples in FIGS. 1A and 1B, the deflection of the cantilever 16 ismeasured by reflecting a laser beam 26 off the back side of cantilever16 and towards a position sensitive detector 28.

One of the continuing concerns with these devices is how to improvetheir accuracy. Since these microscopes often measure surfacecharacteristics on the order of Ångstroms, positioning the sample andprobe with respect to each other is critical. Referring to FIG. 1C, asimplemented in the arrangement of FIG. 1A, when an appropriate voltage(V_(x) or V_(y)) is applied to electrodes 29 disposed on the upperportion 30 of piezoelectric tube actuator 18, called an X and Y-axistranslating section or more commonly an “X-Y tube,” the upper portionmay bend in two axes, the X and Y-axes as shown. When a voltage (V_(z))is applied across electrodes 29 in the lower portion 32 of tube 18,called a Z-axis translating section or more commonly a “Z-tube,” thelower portion extends or retracts, generally vertically. In this manner,portions 30, 32 and the probe (or sample) can be steered left or right,forward or backward and up and down. This arrangement provides threedegrees of freedom of motion. For the arrangement illustrated in FIG.1A, with one end fixed to a microscope frame (for example, 34 in FIG.1D), the free end of tube 18 can be moved in three orthogonal directionswith relation to the sample 20.

Unfortunately, piezoelectric tubes and other types of actuators areimperfect. For example, the piezo tube often does not move only in theintended direction. FIG. 1D shows an undesirable, yet common, case wherea piezo tube actuator 18 was commanded to move in the Z-direction (bythe application of an appropriate voltage between the inner and outerelectrodes, 29 in FIG. 1C), but where, in response, the Z-tube 18 movesnot only in the Z-direction, but in the X and/or Y-directions as well.This unwanted parasitic motion, shown in FIG. 1D as ΔX, limits theaccuracy of measurements obtained by scanning probe microscopes. Similarparasitic motion in the Y-direction is also common. The amount of thisparasitic motion varies with the geometry of the tube and with theuniformity of the tube material, but typically cannot be eliminated tothe accuracy required by present instruments.

Current methods of monitoring the motion of the probe or sample 20 whendriven by a piezoelectric tube are not sufficiently developed tocompensate for this parasitic X and Y-error. The devices are typicallycalibrated by applying a voltage to the X-Y tube and the Z-tube, andthen measuring the actual distance that the probe travels. Thus, theposition of the free end of the piezo tube is estimated by the voltagethat is applied to the X-Y tube and the Z-tube. However, because the(X,Y) position error introduced by the Z-tube on the probe (or on thesample for the arrangement shown in FIG. 1B) is essentially random, itcannot be eliminated merely by measuring the voltage applied to theZ-tube or to the X-Y tube.

Moreover, with respect to movement in the intended direction,piezoelectric tubes and other types of actuators typically do not movein a predictable way when known voltages are applied. The ideal behaviorwould be that the actuator move in exact proportion to the voltageapplied. Instead actuators, including piezo tubes, move in a non-linearmanner, meaning that their sensitivity (e.g., nanometers of motion perapplied voltage) can vary as the voltage increases. In addition, theysuffer from hysteresis effects. Most generally, the response to anincremental voltage change will depend on the history of previousvoltages applied to the actuator. This hysteresis effect, thus, cancause a large prior motion to affect the response of a commanded move,even many minutes later.

Notably, also, vertical measurements in scanning probe microscopy aretypically made by moving the probe up or down in response to the risingor falling sample surface. For example, for AFM operation in tappingmode, the actual vertical measurement is the average distance the probemoves in the vertical direction to maintain a constant oscillationmagnitude as it taps the surface, while for AFM operation in contactmode, the vertical measurement is the distance the probe moves tomaintain a particular amount of force between the cantilever stylus andthe sample surface. This distance is often calculated mathematically byrecording the voltage applied to the piezoelectric tube and thenmultiplying by the tube's calibrated sensitivity in nm/V. But asmentioned previously, this sensitivity is not constant and depends onthe previous voltages applied to the tube. So using the voltage appliedto the tube to calculate the vertical motion of the tube will alwaysresult in an error with respect to the actual motion. This error cantranslate directly into errors when measuring surface topography of asample.

What is needed, therefore, is an apparatus and method for controllingthe motion of the probe or sample to minimize the effects due to, forexample, adverse parasitic motion introduced by an actuator (e.g., aZ-tube) in a metrology apparatus. Moreover, an apparatus is needed tomeasure the magnitude of the intended motion to, for example, trackwhether intended motion is being realized.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method forcontrolling the motion of a metrology probe to minimize negative effectsassociated with parasitic motion introduced, for example, by an actuator(e.g., a Z-tube) in a metrology apparatus such as an SPM or a profiler.In addition, the apparatus measures the magnitude of the actual motion.Notably, the apparatus implements an optical detection apparatus,utilizing an arrangement of reflecting surfaces disposed in corner-cuberetroreflector-like relationship, so that the light reflected and sensedby the apparatus is relatively immune to, for example, lateraldeflections of components of the microscope coupled thereto.

According to first aspect of the preferred embodiment, a Zisolating/measuring assembly for a metrology apparatus includes apiezoelectric or electrostrictive actuator assembly including a firstactuator stage configured to controllably move in first and secondorthogonal directions, and a second actuator stage integrated with orcoupled to the first actuator stage, and being configured tocontrollably move in a third direction orthogonal to the first andsecond orthogonal directions. In addition, the assembly includes areference structure having first and second ends wherein the first endis fixed relative to movement of the second actuator stage. The assemblyalso includes a multi-bar linkage assembly fixed to the second end ofthe reference structure, and a coupling attached to the second actuatorstage and to the multi-bar linkage, wherein the second actuator stageand the coupling move the linkage in the third orthogonal direction in amanner that substantially isolates the linkage from any second actuatorstage motion in the first and second directions.

According to another aspect of the invention, a Z isolating/measuringassembly includes an elongate actuator with a longitudinal axis having afixed end, and a free end configured to translate in three orthogonaldirections with respect to the fixed end. In addition, the assemblyincludes a multiple bar linkage having first and second links mutuallyconstrained to translate with respect to each other, and wherein thefirst link is fixed to a reference structure and the second link isconstrained to translate in a direction parallel to the longitudinalaxis of the actuator. The assembly also has a coupling having first andsecond ends, the first end being fixed to the actuator proximate to itsfree end, and the second end being fixed to the second link, thecoupling adapted to transmit force and therefore displacement in adirection substantially parallel to the longitudinal axis of theactuator.

According to yet another aspect of the invention, a method of reducingpositioning errors at the free end of an elongate actuator of ametrology apparatus includes the step of supporting a probe assembly ona probe support assembly. In addition, the method includes supportingthe probe support assembly at a first end to a reference structure ofthe metrology apparatus, the reference structure being substantiallyinsensitive to longitudinal expansion or contraction of the elongateactuator. The method further includes isolating the reference structurefrom a longitudinal tube deflection of the actuator. When driving theactuator, the metrology apparatus simultaneously generates bothlongitudinal deflections as well as lateral deflections in thelongitudinally expanding and contracting portion. The method operates toprevent the lateral deflections generated in the longitudinallyexpanding and contracting portion of the tube from laterally deflectingthe probe support assembly, while simultaneously transmitting thelongitudinal deflections to the probe support assembly.

According to yet another aspect of the preferred embodiment, anapparatus for measuring movement of an actuator in a metrology apparatussuch as a scanning probe microscope (SPM) includes an optical measuringdevice having a light source that generates a light beam, the measuringdevice being configured to change the direction of the beam in responseto movement of the actuator. The apparatus also includes a sensor todetect the beam position and generate a signal indicative of themovement of the actuator.

According to another aspect of this embodiment, the measuring deviceincludes a movable bar assembly coupled to the actuator and to areference structure, wherein the bar assembly has a reflecting surfacethat is adapted to deflect the beam. Moreover, the bar assembly isresponsive to movement of the actuator so as to change the direction ofthe deflected beam.

According to a further aspect of the preferred embodiment, a method formeasuring movement of an actuator in a metrology apparatus such as ascanning probe microscope (SPM) includes the steps of providing amovable bar assembly coupled to the actuator and to a referencestructure. Moreover, the method includes measuring, in response tomovement of the actuator, movement of the movable bar assembly, whereinmovement of the movable bar assembly is indicative of movement of theactuator.

According to another aspect of the preferred embodiment, an apparatusfor ensuring that displacement generated by an actuator, and transferredto the cantilevered probe coupled thereto, is isolated from movement ofthe metrology apparatus in a direction other than the intended directionassociated with the actuator, includes a flexure that is coupled to theactuator via a flexible bar or member (i.e., a coupling). The couplingis adapted to transmit displacement only in an intended direction, thusminimizing adverse affects associated with parasitic movement of atleast a portion of the metrology apparatus, such as the actuator. Theapparatus also includes a fixed reference structure to which the flexureis also attached. Preferably, the flexure is a parallelogram flexurecomprising a four bar linkage that is adapted to translate so that itsopposed vertical links remain generally orthogonal to the X-Y plane inresponse to force and therefore displacement transmitted in the verticalor “Z” direction by the coupling, this outcome due at least in part tothe connection of the flexure to the reference structure.

According to a still further aspect of the preferred embodiment, in ametrology apparatus such as a scanning probe microscope (SPM) having anactuator for moving a probe in a particular direction, a referenceassembly that generally decouples movement in a direction other than theparticular direction from the probe, the reference assembly including areference structure and a probe support assembly coupled to thereference structure and to the actuator, wherein the probe is attachedto the probe support assembly. Further, the apparatus includes aflexible bar having opposed ends, one of which is coupled to theactuator and the other of which is coupled to the probe supportassembly, wherein the flexible bar, the reference structure, and theprobe support assembly are adapted to collectively decouple movement ofthe metrology apparatus in a direction other than the particulardirection from the probe.

Moreover, the flexible bar is preferably more flexible in response todisplacements applied thereto in any direction other than the particulardirection than to a displacement applied in the particular direction.

These and other objects, features, and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription and the accompanying drawings. It should be understood,however, that the detailed description and specific examples, whileindicating preferred embodiments of the present invention, are given byway of illustration and not of limitation. Many changes andmodifications may be made within the scope of the present inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of the invention is illustrated in theaccompanying drawings in which like reference numerals represent likeparts throughout, and in which:

FIG. 1A is a partial side elevational view of a prior art atomic forcemicroscope utilizing a scanned stylus and including a three-axispiezoelectric actuator assembly;

FIG. 1B is a partial side elevational view of a prior art atomic forcemicroscope utilizing a scanned sample and including a three-axispiezoelectric actuator assembly;

FIG. 1C is a perspective view of a prior art piezoelectric tube actuatorof an atomic force microscope;

FIG. 1D is a front elevational view illustrating parasitic motion of apiezoelectric actuator assembly configured to move in a predetermineddirection, in this case “Z”;

FIG. 2 is a side elevational view of a scanning probe microscopeassembly according to the present invention;

FIG. 3 is a side elevation partial cross-sectional view of an opticaldetection apparatus for measuring the intended motion of a piezoelectricactuator according to the present invention;

FIGS. 3A-3C illustrate alternate embodiments of the optical detectionapparatus shown in FIG. 3;

FIG. 4 is a partial side elevation cross-sectional view of an apparatusfor decoupling movement of the microscope in a direction other than aparticular intended direction from a probe assembly of a scanning probemicroscope, according to the present invention;

FIG. 5 is a side elevation cross-sectional view of the piezoelectricactuator assembly shown in FIG. 2;

FIG. 6 is an enlarged perspective view of the lower portion of thepiezoelectric actuator assembly of FIG. 5;

FIG. 7 is a partial side elevation cross-sectional view of the lowerportion of the piezoelectric actuator assembly shown in FIG. 5,illustrating movement of the actuator, and corresponding movement of theflexure, in phantom;

FIGS. 8A and 8B illustrate alternate embodiments of the apparatus shownin FIG. 4;

FIG. 9 is a partial side elevation cross-sectional view of an alternateembodiment of the present invention; and

FIG. 10 is a schematic diagram of a control circuit configured tomonitor the radiation detectors, control the piezoelectric actuator andsave data indicative of the three-dimensional location of scan points onthe surface of the sample.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 2, a scanning probe microscope (SPM) 100 isshown. The microscope includes a chassis including a support 102 towhich an actuator assembly 104 is attached. In addition, a sample base106 is fixed to support 102 and is configured to accommodate a sample108. The actuator assembly 104 includes an actuator 110, a referenceassembly 111 comprising, among other structure, an elongate referencestructure 112 that surrounds actuator 110, and a probe assembly 113.Preferably, reference structure 112 is tubular and has a longitudinalaxis that is generally collinear with the longitudinal axis of actuator110. Notably, actuator 110 can be piezoelectric or electrostrictive, andcan be a tube actuator or another type of actuator conventional in theart of nanopositioning systems.

At a lower free end 105 of actuator assembly 104, a probe assembly 113is attached and includes a cantilever 114 having a stylus 115 attachedthereto. During operation, stylus 115 is scanned across the surface ofsample 108 to determine surface characteristics (e.g., topography) ofthe sample. The scanning operation is provided by actuator 110, which isdriven by program-controlled signals (e.g., appropriate voltages) tocause the actuator 110 to move laterally in two dimensions across thesurface of sample 108, as well as to extend and retract the probeassembly 113, i.e., to move cantilever 114 toward or away from thesample, typically in response to closed loop signals derived from sensor109. As a result, the actuator 110 preferably can translate thecantilever 114 in three orthogonal directions under program control.Note that for convenience we will refer to the extending and retractingof the probe assembly 113 toward and away from sample 108 as motion inthe Z-direction, and translation laterally across the surface of thesample as motion in the X-direction and the Y-direction, where the X andthe Y-axes are orthogonal to each other and define a plane substantiallyparallel to the surface of sample 108. This nomenclature is used purelyfor convenience to indicate three orthogonal directions.

Next, to illustrate different aspects of the preferred embodiment, weinitially turn to FIG. 3, which shows a measuring apparatus formonitoring movement of a piezoelectric Z-tube 222 of an actuator 110. Anoptical measuring device 120 includes a steering mechanism 122 andcouples actuator 110 to a reference frame 124, the frame being fixedrelative to actuator 110. In addition, steering mechanism 122 acts as aprobe support assembly to which a probe assembly (not shown) isattached. In operation, a beam of electromagnetic radiation such aslight “L” is generated by a light source 126 and is directed at steeringmechanism 122. Steering mechanism 122 changes the direction of the lightbeam in response to movement of actuator 110. This change in directionof the beam is detected by a detection sensor 128 and, because in thiscase tube 222 is a Z-tube, the change in direction of the beam isindicative of vertical actuator movement.

More particularly, steering mechanism 122 includes a movable barassembly having a coupling bar or first link 130 having a first endattached to Z-tube 222 and a second end 132. Steering mechanism 122 alsoincludes a movable bar or second link 134 having opposed ends, the firstof which is rotatably attached to the second end 132 of link 130 at afirst pivot point 133. The opposite end of the movable bar 134 isrotatably attached to fixed reference frame 124 at point 136. Movablebar 134 defines a surface 138, which is adapted to reflect light beam“L.” A second reflecting surface preferably comprises a fixed mirror 140attached at an angle to an inner surface 142 of fixed reference frame124 to deflect incoming light beam “L” towards movable bar 134.Moreover, to accommodate the light beam, fixed reference frame 124includes a first aperture 144 adapted to receive the incoming lightbeam, and a second aperture 146 adapted to allow passage of the beam,after being reflected by bar 134, through fixed reference frame 124 andtowards detector 128.

In operation, in response to actuation of actuator 110 (for example, inthe Z-direction marked “A” in FIG. 3), movement of the actuator istransferred to movable bar 134 via coupling bar 130. This causes themovable bar 134 to rotate generally in a clockwise fashion about secondpivot point 136. As a result, the steered beam is deflected towardsdetector 128 at an angle different than when Z-tube 222 is not actuated.This change in the direction of the light beam “L” is depicted by thepath marked “B” in FIG. 3 and is indicative of the amount of actuatormovement. More particularly, as the actuator 110 is used to move theprobe (not shown, but preferably coupled to a bottom surface 139 ofmovable bar 134) in the Z direction, the amount of movement in theZ-direction is sensed by the system by noting the position at which thedeflected light beam contacts the sensor 128.

Turning to FIGS. 3A-3C, alternate embodiments of the measuring device120 as illustrated in FIG. 3 are shown. In FIG. 3A, measuring device 150includes a light source 126 that is fixed relative to a piezoelectricactuator assembly 152 that comprises an upper X-Y actuator portion orstage 154 coupled to a lower Z-tube actuator portion or stage 156. Inthis case, movement of Z-tube 156 is being monitored.

Measuring device 150 also includes a lens 158 that is coupled to Z-tube156. Notably, light source 126 is positioned such that lens 158 isintermediate the light source and a sensor 128 disposed at a positiongenerally opposite the light source 126. In operation, as Z tube 156 isactuated and caused to move in a particular direction (in this case“Z”), lens 158 correspondingly moves. Because sensor 128 is fixed, as islight source 126, measuring the position at which the light beam “L”output by lens 158 contacts sensor 128 is indicative of the movement ofthe actuator 152. Preferably, the magnification of the lens equals,

M=1+i/o  Eqn. 1

where “i” is the orthogonal distance from sensor 128 to lens 158, and“o” is the orthogonal distance from lens 158 to light source 126.

Turning to FIG. 3B, light source 126, rather than the lens 158 as inFIG. 3A, is mounted to the actuator 152 whose movement is to be measured(in this case the “Z” actuator 156). In this embodiment, a measuringdevice 151 includes light source 126 attached to actuator 156 via amount 162, and a sensor 128 is included which is fixed relative to theactuator 152 and the light source 126. In addition, a lens 164 ispositioned intermediate light source 126 and sensor 128 and has amagnification generally equal to,

M=i/o  Eqn. 2

where “i” is the orthogonal distance between lens 164 and the sensor128, and “o” is the orthogonal distance between light source 126 andlens 164. As the Z-tube is actuated, light source 126 moves inconjunction with it, thus causing light passing through lens 164 to bedirected at a point displaced from the point at which the light isdirected on sensor 128 when Z-tube 156 is not actuated. Sensor 128detects this displacement and generates a corresponding signalindicative of the amount of actuator 156 movement.

In yet another alternate embodiment of the optical measuring device,shown in FIG. 3C, a measuring device 153 directs a light beam “L”between actuator 110 (e.g., a piezoelectric tube 222) and fixed frame124 (which is preferably tubular and surrounds actuator 110) in adirection generally parallel to the longitudinal axes of actuator 110and tubular fixed frame or reference structure 124. Measuring device 153includes a link 170 having opposed ends, the first of which is coupledto actuator 110 (for example, a Z actuator) at a first pivot point 174,and the second of which is pivotably coupled to fixed frame 124 at asecond pivot point 176. In operation, the light beam “L” is directedtowards link 170, which comprises reflective surface 178, such that thebeam is reflected towards the inside surface 142 of fixed frame 124.Similar to the embodiment shown in FIG. 3, fixed frame 124 is configuredto include an aperture 180 to allow passage of the reflected beam so asto allow impingement of the beam on sensor 128. As the actuator 110 isactivated, link 170 rotates and the angle at which the beam is reflectedchanges, thus causing the reflected or output beam to impinge upon thesensor 128 at a different location than when the actuator is notactivated. This different position detected by sensor 128 is indicativeof the amount of displacement of the actuator 110, as discussedpreviously.

Turning to FIG. 4, an apparatus 200 is illustrated for ensuring thatdisplacements generated by an actuator, and transferred to thecantilevered probe coupled thereto, are isolated from movement of theactuator in a direction other than the intended direction of theactuator, e.g., isolated from parasitic movement of the actuator.Generally, an actuator 110 is coupled to a flexure 204 via a flexiblebar or member (i.e., a coupling) 206 that is adapted to transmitdisplacement only in an intended direction, thus minimizing adverseaffects associated with parasitic movement of the metrology apparatus,such as actuator 110. In FIG. 4, for example, actuator 110 is preferablya Z tube actuator. Therefore, in that case, coupling 206 is configuredso as to transmit displacement generated by actuator 110 in the Zdirection, but generally not in the X and Y directions. Note that theremaining discussion of FIG. 4 assumes actuator 110 is a Z-tubeactuator.

Next, apparatus 200 includes a fixed reference structure 208 to whichflexure 204 is also attached. Flexure 204 is preferably a parallelogramflexure comprising a four bar linkage that is adapted to translate sothat its opposed vertical links 210, 212 remain generally orthogonal tothe X-Y plane in response to force and therefore displacementtransmitted in the vertical or “Z” direction by bar 206. This movementof flexure 204 is rotation about points 215, 216, 217 and 218 thereof,as described in further detail below in conjunction with FIG. 7.

Again, to ensure that the opposed vertical links of the flexure 204 movein this fashion, the flexible element 206 is configured so as to besufficiently rigid to transmit vertical displacements of actuator 110,but flexible enough to decouple, for example, the parasitic X-Y movementof the actuator 110 from the flexure 204. Flexible element 206 may be onthe order of 3 mm long and 0.2 mm in diameter, for instance. A probe 214is coupled to link 210 of flexure 204. As a result, probe 214 of the SPMmoves substantially only in the intended direction in response toactivation of actuator 110, in this case Z. Because in a preferredembodiment reference structure 208 is coupled to an X-Y actuatorassembly (e.g., 220 in FIG. 5), reference structure 208 moves inconjunction therewith, thus transmitting this intended X-Y motion toflexure 204. As a result, probe 214 can move in the X and Y-directions.Notably, this intended X-Y motion is not inhibited by bar 206 becausebar 206 is generally flexible in response to displacements directed inthe X and Y-directions. Such a decoupling arrangement is employed in theAFM shown in FIGS. 2, 5, and 7, and therefore a more specificdescription of the apparatus and its operation is provided inconjunction therewith immediately below.

Referring to FIGS. 2 and 7, an electromagnetic radiation source 126(e.g., a laser) is fixed to support 102. In operation, source 126directs light towards a lower portion 105 of actuator assembly 104,while detector 128 receives light from light source 126 after it hasreflected off this lower portion 105 so as to monitor the amount ofactuator movement. Electromagnetic radiation detector 128 is fixedrelative to support 102 as well, and is employed as part of a measuringdevice 300 (alternately, see FIG. 3 at 120, for example) to determinethe amount of translation of at least part of actuator 110.

With more specific reference to FIG. 7, source 126 of measuring device300 may be mounted so as to direct a beam of light generally verticallytoward a mirror 302 positioned to deflect the beam towards the lowerportion 105 of assembly 104. Preferably, a focusing lens 304 is disposedbetween light source 126 and mirror 302. The beam is then deflectedtoward a sensor 128 (e.g., a position sensing photodiode) via mirror306. A cylindrical lens 308 may be disposed between mirror 306 andsensor 128 (or can be located at any point between source 126 and sensor128 as desired) to again enhance precision.

Still referring to FIGS. 2 and 7, to monitor, for example, topographicalchanges on the surface of the sample and provide appropriate feedbackdepending on the mode of SPM operation, an electromagnetic radiationsource 107 (shown in FIG. 2) is faxed to support 102. Source 107generates radiation that is directed through actuator 110 towards amirror 117 supported by a surface of cantilever 114 of probe assembly113. Mirror 117, in turn, directs the radiation toward detector 109(shown in FIG. 2). Mirror 117 may, in the alternative, be a polishedportion of the back (upper) side of the cantilever 114. Detector 109receives the light reflected from probe 114 and, in turn, generates asignal indicative of, for example, the deflection of probe 114, as isconventional in the art.

The entire actuator assembly 104 is shown in more detail in FIG. 5.Again, actuator assembly 104 includes actuator 110 (preferably apiezoelectric tube) and reference assembly 111 which in turn comprisesreference structure 112, coupling mount 228, flexible bar coupling 230,flexure 232, and slotted disk 250 as described in detail below. In thispreferred embodiment actuator 110 is formed of two sections; first, anupper section 220 that is configured to deflect laterally in a planelying perpendicular to the axis of the actuator under program control.For this reason it is termed an X-Y tube. The actuator 110 also includesa lower Z-tube actuator 222 which is adapted to extend or retract in adirection substantially parallel to the longitudinal axis of the tubeunder program control. A discussion of a means for controlling suchactuators can be found, for example, in U.S. Pat. No. 6,008,489 andother related applications.

The two tubes 220, 222 of the piezoelectric actuator 110 are coupledtogether end-to-end proximate to a circular collar 224 that extendsaround and is fixed to the actuator 110. Also, the assembly 104 ispreferably coupled to frame 102 (FIG. 2) of the scanning probemicroscope with a flange 226 that is fixed to the top of X-Y tube 220.In this preferred embodiment, tubular member or elongate referencestructure 112 of reference assembly 111 extends around at least theZ-tube 222 of the actuator 110 and is fixed to collar 224. Collar 224,in turn, is fixed to the actuator 110 at or near the junction of theupper and lower actuator sections. When X-Y tube 220 is driven underprogram control, it deflects in a direction generally perpendicular tothe longitudinal axis. Since collar 224 and hence structure 112 arefixed to the actuator near the bottom of X-Y tube 220, they also deflectlaterally.

On the other hand, when Z-tube 222 is driven under program control itdoes not extend or retract collar 224. Hence structure 112 will notextend or retract since it is coupled to collar 224. Therefore, whenZ-tube 222 extends or retracts, it extends or retracts relative tostructure 112. This causes a substantial change in the relative positionof the two at the lower (or free) end of Z-tube 222.

The semi-circular coupling mount 228 is fixed to the lower end of Z-tube222 and translates together with Z-tube 222 when Z-tube 222 extends andretracts. Reference assembly 111 also includes the flexible bar coupling230 that, in turn, is fixed to coupling mount 228. Bar 230 is configuredso that when Z-tube 222 extends and retracts, the bar correspondinglyextends and retracts with respect to structure 112.

Referring again to FIG. 7, the lower end of flexible bar coupling 230 isfixed to the probe support assembly or flexure 232 of reference assembly111. Flexure 232 is preferably formed out of a solid block of material,and comprises aluminum or a similarly light alloy. The flexure 232 isgenerally in the form of a movable bar assembly or four bar linkage.These links are identified in FIG. 7 as 232A, 232B, 232C and 232D.

Flexible bar coupling 230 is fixed to link 232B of flexure 232. WhenZ-tube 222 retracts in the direction marked “A,” for example, bar 230translates with the free end of Z-tube 222. Because Z-tube 222 isretracting, bar 230 is pulled upwardly toward the upper end of theactuator. This causes link 232B to translate upwardly substantially thesame distance that the end of Z-tube 222 translates upwardly.

Link 232B is supported at flexible joints 233 and 234 to links 232A and232C, respectively. Links 232A and 232C are coupled to link 232D atflexible joints or linkages 236 and 238, respectively. When link 232B ispulled upwardly (again in the direction marked “A”) from a relaxedposition, as shown in phantom in FIG. 7, links 232A and 232C aredeflected upwardly at one end by link 232B. The other end of links 232Aand 232C generally rotate about joints 236 and 238 (also shown inphantom).

Links 232A and 232C are preferably of generally equal length and areparallel to each other. Similarly, links 232D and 232B are preferably ofequal length and parallel to each other. Link 232D is fixed to the lowerend of structure 112. Because structure 112 does not translate upwardlyor downwardly when Z-tube 222 moves upwardly or downwardly (due to itsconnection to collar 224 fixed on actuator 110 above the Z-tube 222) anyexpansion or contraction of Z-tube 222 upwardly or downwardly causes thefour bar linkage of flexure 232 to deflect about joints 233, 234, 236,and 238. Preferably, thickness t₁, of each of the links is approximately0.9 mm, while the thickness t₂ of each of the joints is approximately0.08 mm.

Thus, when the four bar linkage made of the links 232A-D is deflectedupwardly or downwardly, they form a parallelogram arrangement and thereis substantially no rotation of link 232B, only translation. As aresult, link 232B is preferably constrained to simply translate upwardlyor downwardly.

In operation, electromagnetic radiation from source 126 is reflected offa mirror 240 of measuring device 300, mirror 240 being mounted onflexure 232, particularly link 232D. This light is reflected downwardlyand is reflected again, this time off a mirror 242, which is also fixedto flexure 232, particularly link 232C. The light reflected off mirror242 then is directed towards detector 128, which generates a signalindicative of the location at which the reflected light impinges uponthe detector 128. The signal provided by detector 128 changes dependingupon the degree of deflection of the four bar linkage of flexure 232.

More particularly, comparing the relaxed position of the flexure 232 inFIG. 7 to the upwardly deflected position shown in phantom, it is clearthat upward deflection of link 232B causes link 232C to rotate aboutjoint 238. This in turn causes mirror 242 to rotate about joint 238.This movement of mirror 242 causes the light beam to reflect off mirrorat a different angle than when the beam is reflected off the mirror 242when the flexure is in the relaxed position. As a result, the beam movesto a position on the detector 128 which is displaced from the initiallocation of the beam, as shown in phantom. It is this change in theposition of light impinging on detector 128 that causes a change in thesignal generated by detector 128, and hence, provides an indication thatlink 232B has translated upwardly or downwardly with respect to the freeend of structure 112 to which link 232D is fixed.

Notably, mirrors 240 and 242 are preferably disposed with respect toeach other such that the light sensed by detector 128 is substantiallyimmune to lateral deflections of member 112. In the embodiment shown inthe figures, there are several structural elements that individually andcollectively contribute to this immunity. In particular, mirrors 240 and242 are disposed to return light to the detector 128 in a pathsubstantially parallel to the path of the light impinging upon mirror240 of measuring device 300, and thus form what is akin to a corner cuberetro-reflector. As Z-tube 222 moves, mirrors 240, 242 maintain theirgeneral orthogonal relationship, albeit in displaced fashion, thusaffording accurate measurements of Z-displacement. Another feature thatcontributes to this accuracy is the fact that the path of lightimpinging upon mirror 240 and the path of light reflected from mirror242 are substantially parallel to the surface of the sample (108 in FIG.2).

When structure 112 is deflected laterally across the surface of thesample, by activation of X-Y tube 220 (FIG. 5) for example, mirrors 240and 242 are also deflected. This occurs whether or not there has beenany upward or downward motion of Z-tube 222 with respect to member 112.Due to the arrangement of the incoming and outgoing beams from mirrors240 and 242 and the orientation of those mirrors with respect to eachother, any lateral deflection will not substantially change the signalimpinging on detector 128, and detector 128 will continue to generate asignal indicative of the height of the flexure 232 (and particularlylink 232B), and therefore the probe above the sample generally withouterror.

The above-described apparatus is thus used to isolate the movement ofZ-tube 222 in its intended Z-direction, yet permit free lateral motionof the lower end 105 of actuator assembly 104. At the lower end ofactuator assembly 104, reference assembly 111 includes slotted disk 250having four mounting pins 252 (see FIG. 6), the slotted disk being fixedto the lower portion of link 232B. Next, probe assembly 113 includes aprobe base 101 (shown in FIG. 7 in phantom lines) that can be plugged orunplugged from pins 252 to hold the probe base 101 onto the slotted disk250. Probe assembly 113 also includes cantilever 114 fixed on one end tothe probe base 101, and a stylus 115 attached to the free end ofcantilever 114.

Referring again to FIGS. 2 and 7, light source 107 (shown in FIG. 2)generates light which travels down through the actuator 110, and isreflected off mirror 117 and returns to detector 109 (shown in FIG. 2).Whenever cantilever 114 is flexed upwardly or downwardly about itsmounting point, mirror 117 rotates about the fixed end of cantilever 114and causes the light generated by source 107 to move with respect todetector 109. This movement, in turn, causes a change in the signalgenerated by detector 109 that indicates a change in the amplitude ofthe deflection of cantilever 114, and hence a change in the force and/ordistance relationship of the probe assembly 113 and the sample surface108.

Typically, to determine the height of various features at differentlocations on the sample surface, probe assembly 113 is moved laterallyacross the surface of the sample 108. In operation, to direct the probelaterally, an electrical signal is applied to X-Y tube 220 (FIG. 5),which in turn causes the lower portion 105 of the actuator assembly 104to deflect in relation to the sample. Depending upon the signals appliedto X-Y tube 220, this can cause probe assembly 113 to move in twoorthogonal directions across the surface of the sample.

In an alternative embodiment of an apparatus for isolating “Z,” ratherthan using a parallelogram flexure as shown in FIGS. 4 and 7, adisc-shaped flexure or membrane 310 is employed, as shown in FIG. 8A.Membrane 310 is coupled to a reference structure 112 around itsperimeter and has a circumferential joint or trench 312 that defines aperimeter flexure region. Further, membrane 310 has a bottom surface 314to which the probe assembly (for example, 113 in FIG. 2) can beattached. Membrane 310 allows vertical forces to be transmitted to theprobe assembly, due to “flexing” of membrane 310 at trench 312 inresponse to these forces, yet decouples X-Y motion of the Z-tube 222 toensure that movement of the probe assembly caused by the Z-actuatorremains in Z.

A coupling element or member 230, which in operation is generallyflexible in response to displacements directed in the X andY-directions, for example, and is generally stiff in response todisplacement directed in the Z-direction, is used to couple the actuator110 to membrane 310. Because membrane 310 is coupled to the referencestructure 112 around its entire circumference, membrane 310 is generallynon-responsive to displacements directed orthogonally to thelongitudinal axis of actuator 110, thus decoupling these displacementsfrom the probe assembly. Notably, these displacements in the X andY-directions are absorbed by flexible coupling member 230, thusminimizing the effects of parasitic movement of Z-tube 222. To thecontrary, lateral motion generated by the actuator 110 which istransmitted by structure 112, is transferred to the probe, as required.Ideally, membrane 310, referring to FIG. 8B, may be made of a metal, orpolymer, or other suitable material.

Referring to FIG. 8B, in another alternate embodiment of a flexure forisolating “Z,” similar to that shown in FIG. 8A, a pair of cross wires322, 324 disposed generally orthogonally to one other are attached attheir opposed ends to a mounting ring 326 that, in turn, is attached toa reference structure (for example, 112 in FIG. 8A). Again, a couplingelement or member (230 in FIG. 8A) is employed to couple actuator 110 tothe junction of cross wires 322, 324. Moreover, a probe assembly iscoupled to wires 322, 324 and thus moves in corresponding fashion withwires 322, 324.

Similar to disc-shaped member 310, wires 322, 324 are generally adaptedto decouple displacements directed in the X and Y-directions andtransmit displacement directed in the Z-direction. In operation, wires322, 324 and member 230 interact to couple vertical displacementgenerated by the Z-tube actuator attached thereto to the cantileverprobe attached thereto, yet decouple X-Y displacements of the Z-tubeactuator (these displacements typically being absorbed by member 230) toensure that movement of the probe assembly generally remains in Z.

Turning next to FIG. 9, an alternative embodiment of the actuatorassembly 104 of the present invention is shown. In particular, anactuator assembly 400 decouples X-Y movement (e.g., X-Y movement of anX-Y actuator 220) from the measurement of the amount of verticalmovement produced by Z-actuator 222. Actuator assembly 400 comprises anactuator 110 which in turn preferably comprises a piezoelectric tubeactuator, a reference assembly 401, and a probe assembly (not shown).Moreover, piezoelectric tube actuator comprises X-Y tube 220 and Z-tube222.

Reference assembly 401 includes a circular mount 402 having a clamp 404and a rod 406 having a longitudinal axis generally parallel to, anddisplaced from, the longitudinal axis of tube actuators 220, 222. Clamp404 is employed to couple a first end 408 of rod 406 to a coupler 224 ofactuator 110. A second end 410 of rod 406 is coupled to a flexure 412 ofreference assembly 401. Flexure 412 is, in turn, coupled to Z-tube 222.Flexure 412 includes two joints 414, 416. In addition, mirrors 418, 420are attached to flexure 412 such that their reflecting surfaces aregenerally orthogonal to one another, thus forming a structure akin to acorner-cube retro-retroreflector, similar to that described above inconjunction with FIG. 7. Preferably, reflecting elements 418, 420 arefront surface mirrors.

In operation, a light beam generated by a source 126 is directed atmirror 420 which reflects the beam towards mirror 418 which, in turn,reflects the beam towards detector 128 for measuring the amount ofvertical deflection. As Z-tube 222 is actuated, the portion of flexure412 having mirror 418 on it rotates about joints 414, 416 such thatmirror 418 reflects the beam at an angle indicative of the amount of themovement. Most notably, lateral movement of actuator 110 (for example,generated by X-Y tube 220) for scanning a sample (not shown) isdecoupled from this Z-measurement. In particular, rod 406 is independentof movement of the Z-tube 222 because it is attached at clamp 404 at apoint on actuator 110 above the top of Z-tube 222. As a result, rod 406moves when X-Y tube 220 is actuated but not when Z-tube 222 is actuated.When flexure 412 rotates about joints 416, 418 in response to verticalmovement of Z-tube 222, vertical movement of the probe can be accuratelymeasured notwithstanding simultaneous movement caused by X-Y tube 220.This is primarily due to the mirrors 418, 420 always generallymaintaining their orthogonal relationship. As a result, the measurementof Z is isolated from X-Y movement generated by tube 220.

Next, to determine the height of the surface, the height of the probeabove (or in contact with) the surface must be monitored and controlled.

Referring again to FIGS. 2 and 7, in one mode of operation, the stylus115 is in contact with the sample, and slight deflections of thecantilever 114 caused by its moving over the sample are measured. Thisis called “contact” mode. As the stylus 115 is deflected upwards, itmoves cantilever 114 and mirror 117. This change in the position ofmirror 117 causes the reflected light to move across detector 109 (shownin FIG. 2). The output of the detector 109 is fed back to the Z-tube222. Thus, flexing of the cantilever 114 is a function of the signalprovided by detector 109. In typical operation, the amount of flexing ofcantilever 114 is maintained constant by extending or retracting Z-tube222 (e.g., lengthening or shortening) in response to a signal based onthe output of the detector 109. When the stylus 115 reaches a surfaceasperity that causes the cantilever 114 to flex upward, thereforedeflecting light with respect to detector 109, the SPM attempts torestore the cantilever 114 to the same position on or above the surfaceof the sample. This capability is provided by data acquisition andcontrol module 500 shown in FIG. 10, that extends or retracts Z-tube 222in order to restore cantilever 114 to its original deflection.

In Tapping Model™ operation, an oscillator (not shown) causes the freeend of cantilever 114 to oscillate up-and-down, typically at or near itsresonant frequency. As probe assembly 113 approaches the surface of thesample, interaction between the surface 108 and the stylus 115 causesthe amplitude (or phase) of these oscillations to change. The angle ofthe radiation reflected from mirror 117 changes in amplitude accordinglyand causes a change in the location of the reflected light incident upondetector 109. Detector 109, in turn, generates a signal indicative ofthe changed amplitude and provides this signal to the control circuitryshown in detail in FIG. 10. The control circuitry in turn provides acontrol signal to Z-tube 222 to adjust its length to move the stylus 115up or down until the cantilever 114 returns to the desired oscillationamplitude. The control signal is thus indicative of surface features ofthe sample 108.

Referring still to FIG. 10, a control circuit 500 is shown connected tosections 220 and 222 of an actuator 110, such as a piezoelectric tubeactuator, detectors 128 and 109, and sources 126 and 107. Controlcircuit 500 includes data acquisition and control module 502 which iscoupled to and drives actuator drivers 504 and, source drivers 506.Actuator drivers 504 are in turn coupled to tube actuators 220 and 222of actuator 110. These drivers 504 generate high voltage signalsnecessary to cause X-Y tube 220 to move laterally and Z-tube 222 toexpand and contract vertically. Source drivers 506 are coupled to anddrive radiation sources 126 and 107. Control module 502 is also coupledto and receives signals from detector signal conditioner 508. Signalconditioner 508 receives the raw signals from the two radiationdetectors 128, 109 and converts them into signals that can be read bycontrol module 502.

Control module 502 includes a series of instructions that controls theoperation of control circuit 500 and hence, the operation of actuator110. This includes instructions that receive and process signalstransmitted from detector signal conditioners 508 that are indicative ofthe radiation falling on detectors 109 and 128. The instructions alsoinclude instructions that transmit appropriate signals to actuatordrivers 504 causing actuator drivers 504 to generate the appropriatehigh voltage signals to tubes 220 and 222 of actuator 110. Module 502also includes instructions to generate signals and transmit them tosource drivers 506 causing source drivers 506 to properly control theradiation emitted by sources 107 and 126.

Control module 502 monitors changes in the signal generated by detector109 and determines, based upon changes in the signal, that thecantilever 114 has been deflected, either upwardly or downwardly incontact mode, or that its amplitude of oscillation, in Tapping Mode®,has increased or decreased. In response to this signal, the controller502 attempts to raise or lower the probe assembly 113 until the signalgenerated by detector 109 returns to its original level. To do this, thecontrol module 502 generates a signal and applies it to Z-tube 222 ofthe piezoelectric tube actuator 110, which in turn causes it to contractor expand depending on the signal. This contraction or expansion pullsflexible bar coupling 230 upwardly or downwardly, which in turn pullslink 232B upwardly or pushes it downwardly, respectively. Link 232B ismechanically coupled to the fixed end of cantilever 114 causing it tomove with bar 230. This motion of the fixed end of cantilever 114 causesmirror 117 to be restored to its original orientation, and hence, causesthe light falling on detector 109 to generate its original signallevels. These restored signal levels are sensed by control module 502which then stops changing the signal applied to Z-tube 222. In summary,the height information is interpreted from the voltage fed to the Z-tube222. Specifically, the voltage fed to the Z-tube 222 as part of theusual feedback process of maintaining a constant cantilever amplitude ordeflection is also read by the data acquisition and control module 502as an indication of sample asperity height.

In accordance with the novel principles of the present invention,accurate Z-height information is independently derived from detector 128while the usual feedback process described above continues.Specifically, the control module 502 uses the signal provided bydetector 128 to determine the height of probe assembly 113 in thefollowing manner. Again, we will assume that the stylus 115 is beingtranslated across the surface of sample 108 and reaches an asperity. Asin the previous case, this will flex cantilever 114 upwardly in contactmode or reduce the amplitude of oscillation of the cantilever 114 inTapping Mode® and cause the signal to change at detector 109. Again, thecontroller 502 will cause section 222 to contract by changing the signalapplied to it. This, in turn, causes flexure 232 to move upwardly. Asshown in FIG. 7, this upward motion causes mirror 242 to deflectdownwardly and outwardly away from mirror 240 and causes the lightgenerated by source 126 to fall on a different portion of detector 128.The signal that falls on detector 128 is a function of the height offlexure 232, and hence t he height of the fixed end of cantilever 114.In this case, therefore, controller module 502 reads the signalgenerated by detector 128 and determines the height of flexure 232 (andhence, probe assembly 113) directly.

The preferred embodiment also avoids another positional error due tolateral deflection of Z-tube 222 when it contracts or expands. It isimportant in most measuring processes to determine not only the heightof the surface of sample 108, but also the location at which that heightmeasurement occurred. As we explained in the background of theinvention, Z-tube 222 undesirably deflects laterally when it contractsor expands. Without reference structure 112, this would cause the probeto steer slightly forward, backward, to the left, or to the right acrossthe surface of the sample, rather than moving straight upwardly ordownwardly. Link 232B, which translates upwardly and downwardly togetherwith flexure 232 and the probe itself, is isolated from these lateraldeflections of Z-tube 222. It communicates only the expansion andcontraction of Z-tube 222 to the probe.

The four bar linkage of flexure 232 ensures that the probe itself canonly translate upwardly and downwardly with respect to member 112. It isflexible bar coupling 230 that absorbs this lateral motion and preventsit from being communicated to probe assembly 113 when Z-tube 222 expandsor contracts. Flexible bar coupling 230 has sufficient flexibility thatit can deflect slightly from side to side throughout its length. It isprovided with a length sufficient to permit these lateral deflections ofthe coupling 230 to occur without introducing significant errors intothe system. In this manner, member 112 is isolated from longitudinalmotion of the piezoelectric actuator 110, but will communicate (X,Y)plane motions to flexure 232. Flexible bar coupling 230, flexure 232 andparticularly link 232B are isolated from lateral movement generated bythe expansion and contraction of Z tube 222, yet substantially duplicatethe upward and downward motion of Z-tube 222 and transmit it to probeassembly 113.

The scope of the application is not to be limited by the description ofthe preferred embodiments described above, but is to be limited solelyby the scope of the claims which follow.

What is claimed is:
 1. An assembly for a metrology apparatus, theassembly comprising: an actuator including a first actuator stageconfigured to controllably move in first and second orthogonaldirections, and a second actuator stage adjacent to said first actuatorstage and configured to controllably move in a third directionorthogonal to the first and second orthogonal directions; a referencestructure having first and second ends wherein the first end is fixedrelative to movement of said second actuator stage; a multi-bar linkageassembly fixed to said second end of the reference structure; and acoupling coupled to said second actuator stage and to said multi-barlinkage, wherein said second actuator stage and the coupling areconfigured to move said linkage in the third orthogonal direction in amanner that substantially isolates the linkage from any second actuatorstage motion in the first and second directions.
 2. The assembly ofclaim 1, wherein said actuator is tubular in shape, having asubstantially circular cross section.
 3. The assembly of claim 2,wherein the first and second orthogonal directions lie in a planeperpendicular to a longitudinal axis of said first actuator stage. 4.The assembly of claim 3, wherein said reference structure issubstantially coaxial with said actuator.
 5. The assembly of claim 1,wherein said multi-bar linkage is a four bar parallelogram with twopairs of substantially parallel links.
 6. The assembly of claim 5,wherein said multi-bar linkage further includes four flexible joints,and further wherein said four linkages and said four joints are machinedout of a solid block of linkage material.
 7. The assembly of claim 6,wherein at least one of said links of said multi-bar linkage includes amirror that is deflected about at least one of said four joints wheneversaid second actuator stage extends or retracts.
 8. The assembly of claim1, wherein the metrology apparatus is a scanning probe microscope. 9.The assembly of claim 1, wherein said actuator is a piezoelectricactuator.
 10. An assembly comprising: an actuator with a longitudinalaxis having a fixed end, and a free end configured to translate in threeorthogonal directions with respect to said fixed end; a multiple barlinkage having first and second links mutually constrained to translatewith respect to each other, and wherein said first link is fixed to areference structure and said second link is constrained to translate ina direction generally parallel to the longitudinal axis of saidactuator; and a coupling having first and second ends, said first endbeing fixed to said actuator proximate to its free end, and said secondend being fixed to said second link, the coupling adapted to transmitdisplacement in a direction substantially parallel to the longitudinalaxis of said actuator.
 11. The assembly of claim 10, wherein saidactuator has a Z-axis translating section, and an X and Y-axistranslating section disposed between said fixed end and said Z-axistranslating section.
 12. The assembly of claim 11, wherein saidreference structure is mechanically independent from translation of saidz-axis translating section, but mechanically responsive to said X andY-axis translating section.
 13. The assembly of claim 12, wherein saidreference structure is fixed to said multiple bar linkage to deflectsaid multiple bar linkage in X and Y-directions in response to X andY-deflections of said X and Y-axis translating section.
 14. The assemblyof claim 13, wherein said multiple bar linkage further includes a firstmirror fixed to at least one of said links of the multiple bar linkage,and a second mirror fixed to another of said links of said multiple barlinkage.
 15. The assembly of claim 14, wherein the assembly is adaptedto be supported in a chassis, and further wherein said first mirror isdisposed in the path of a light beam from a light source mounted on saidchassis and is disposed to reflect the light toward said second mirror.16. The assembly of claim 15, wherein said assembly and said chassistogether define a scanning probe microscope.
 17. The assembly of claim10, wherein said actuator is a piezoelectric actuator.
 18. In anassembly for a metrology apparatus having a probe assembly, the assemblyincluding an elongate actuator with a longitudinal axis and having afirst end configured to be coupled to a frame of the microscope and afree end configured to be coupled to the probe assembly, wherein theelongate actuator is configured to provide controllable translation inthree orthogonal directions upon application of proper electricalstimuli, a method of reducing positioning errors at the free end of theelongate actuator comprising the steps of: supporting the probe assemblyon a probe support assembly; supporting the probe support assembly at afirst end of the probe support assembly to a reference structure of themetrology apparatus, the reference structure being substantiallyinsensitive to longitudinal expansion or contraction of the elongateactuator; isolating the reference structure from a longitudinal tubedeflection of the elongate actuator; driving a longitudinally expandingand contracting portion of the elongate actuator; simultaneouslygenerating both longitudinal deflections as well as lateral deflectionsin the longitudinally expanding and contracting portion as a result ofsaid driving step; and preventing the lateral deflections generated inthe longitudinally expanding and contracting portion of the elongateactuator from laterally deflecting the probe support assembly whilesimultaneously transmitting the longitudinal deflections to the probesupport assembly.
 19. The method of claim 18, wherein a second portionof the elongate actuator is configured to provide translation in a planesubstantially perpendicular to the longitudinal direction, and whereinthe method further includes the steps of: driving the second portion ofthe elongate actuator; generating lateral deflections in the secondportion as a result of said driving the second portion step; andtransmitting the lateral deflections in the second portion to the probesupport assembly.
 20. The method of claim 18, further comprising thestep of monitoring a deflection of the probe support assembly whilesubstantially simultaneously monitoring a deflection of the probeassembly.
 21. A scanning probe microscope assembly, comprising: amicroscope frame; a piezoelectric actuator having a first end fixed tosaid frame and a second free end wherein, said piezoelectric actuator ismovable in three orthogonal directions; a first reflector assembly fixedto a reference structure proximate to said free end of saidpiezoelectric actuator; a first electromagnetic radiation source fixedwith respect to said frame and disposed to direct radiation onto saidfirst reflector assembly; a first electromagnetic radiation detectordisposed to receive light from said first source after said light hasbeen received and reflected by said first reflector assembly and togenerate a signal indicative of a degree of longitudinal deflection ofsaid piezoelectric actuator; and wherein said piezoelectric actuatorcannot move said reference structures in at least one of the threeorthogonal directions.
 22. The scanning probe microscope assembly ofclaim 21, further comprising a cantilevered probe having a free end anda fixed end and fixed at its fixed end to said second free end of saidpiezoelectric actuator, said probe including a second reflector disposedto translate with said probe when said probe is deflected with respectto said piezoelectric actuator.
 23. The scanning probe microscopeassembly of claim 22, further comprising a second electromagneticradiation detector disposed to receive light reflected from said secondreflector and to generate a signal indicative of a degree of deflectionof said free end of said probe with respect to said fixed end of theprobe.
 24. An apparatus for measuring movement of an actuator in ametrology apparatus, the measuring apparatus comprising: an opticalmeasuring device including a light source that generates a light beam,said measuring device being configured to change the direction of saidbeam in response to movement of the actuator; a reference structurecoupled to at least a portion of the actuator; a sensor to detect saidbeam and generate a signal indicative of the movement of the actuator;and wherein the actuator is movable in three orthogonal directions. 25.The apparatus of claim 24, wherein said light source is a laser.
 26. Theapparatus of claim 24, wherein said measuring device includes a movablebar assembly coupled to the actuator and to said reference structure,said bar assembly having a reflecting surface that is adapted to deflectsaid beam, and wherein said bar assembly is responsive to movement ofthe actuator so as to change the direction of said deflected beam. 27.The apparatus of claim 26, wherein said bar assembly includes a firstlink having a first end attached to the actuator and a second end, and asecond link defining said reflecting surface and having a first opposedend rotatably attached to said second end and a second opposed endrotatably attached to said reference structure.
 28. The apparatus ofclaim 26, wherein said reference structure is tubular and generallysurrounds the actuator.
 29. The apparatus of claim 28, wherein saidreference structure is configured to allow said light beam and saiddeflected beam to pass therethrough.
 30. The apparatus of claim 29,wherein said reference structure has an inner surface.
 31. The apparatusof claim 30, further including a reflective surface fixed to said innersurface to steer said beam toward said reflecting surface.
 32. Theapparatus of claim 26, wherein said bar assembly includes a link havingopposed ends, a first opposed end rotatably attached to the actuator anda second opposed end rotatably attached to said reference structure. 33.The apparatus of claim 26, wherein said bar assembly comprises a fourbar linkage including first and second reflecting surfaces, saidsurfaces disposed to reflect light such that the incoming and outgoingbeams are generally parallel.
 34. The apparatus of claim 24, whereinsaid optical measuring device includes a lens disposed intermediate saidlight source and said sensor.
 35. The apparatus of claim 34, whereinsaid lens has a magnification equal to 1+i/o, wherein “i” equals theorthogonal distance between said lens and said sensor, and “o” equalsthe orthogonal distance between said lens and said light source.
 36. Theapparatus of claim 34, wherein said light source is mounted to theactuator.
 37. The apparatus of claim 36, wherein said lens has amagnification equal to i/o, wherein “i” equals the orthogonal distancebetween said lens and said sensor, and “o” equals the orthogonaldistance between said lens and said light source.
 38. The apparatus ofclaim 24, wherein the metrology apparatus is a scanning probemicroscope.
 39. The apparatus of claim 24, wherein the actuator is apiezoelectric actuator.
 40. A method for measuring movement of anactuator in a metrology apparatus, the method comprising: providing amovable bar assembly coupled to the actuator and to a referencestructure; and measuring, in response to movement of the actuator,movement of said movable bar assembly, wherein movement of said movablebar assembly is indicative of movement of the actuator.
 41. The methodof claim 40, wherein said movable bar assembly includes a first linkhaving a first end attached to the actuator and a second end, and asecond link defining said reflecting surface and having a first opposedend rotatably attached to said second end and a second opposed endrotatably attached to said reference structure.
 42. An apparatus formeasuring movement of an actuator, the apparatus comprising: an opticalmeasuring device including a source of electromagnetic radiation thatgenerates a beam; a reference structure coupled to at least a portion ofthe actuator; a sensor that detects a position of said beam; and whereinthe actuator is movable in three orthogonal directions but cannot movesaid reference structure in at least one of the three orthogonaldirections, and wherein, in response to movement of the actuator, saidoptical measuring device changes the position of said beam.
 43. Theapparatus of claim 42, further including a reference frame wherein saidreference frame has a longitudinal axis that is generally co-linear withthe longitudinal axis of the actuator.
 44. The apparatus of claim 43,wherein said measuring device includes a movable bar assembly that isattached to said actuator at a first end of said bar assembly, and isattached to said reference frame at a second end of said bar assembly,and wherein said bar assembly defines a reflecting surface that reflectssaid beam towards said sensor.
 45. The apparatus of claim 44, whereinsaid reference frame includes an inner surface and said measuring devicefurther comprises a reflective surface fixed to said inner surface thatsteers said beam towards said reflecting surface, said reflectingsurface deflecting said beam towards said sensor.
 46. The apparatus ofclaim 44, wherein said reference frame is configured to allow said beamand said deflected beam to pass therethrough.
 47. The apparatus of claim42, wherein said source is coupled to the actuator and directs the beamgenerally orthogonally to the movement of the actuator.
 48. Theapparatus of claim 47, wherein said measuring device further includes alens intermediate said source and said sensor to focus said beam towardssaid sensor.
 49. The apparatus of claim 42, wherein said source is fixedrelative to the actuator and directs the beam generally orthogonally tothe movement of the actuator.
 50. The apparatus of claim 42, whereinsaid measuring device includes a lens that moves in conjunction with theactuator.
 51. The apparatus of claim 42, wherein the actuator is apiezoelectric actuator.
 52. In a metrology apparatus having an actuatorfor moving a probe in a particular direction, a reference assembly thatgenerally decouples movement of the apparatus in a direction other thanthe particular direction from the probe, the reference assemblycomprising: a reference structure; a probe support assembly coupled tosaid reference structure and to the actuator, the probe being attachedto the probe support assembly; and a flexible bar having opposed ends,one of which is coupled to the actuator and the other of which iscoupled to the probe support assembly, wherein said flexible bar, saidreference structure, and said probe support assembly are adapted tocollectively decouple movement of the microscope in the direction otherthan the particular direction from the probe.
 53. The apparatus of claim52, wherein said reference structure is a tubular frame and has alongitudinal axis that is generally collinear with the longitudinal axisof the actuator.
 54. The apparatus of claim 52, wherein said flexiblebar is more flexible in response to displacements applied thereto in anydirection other than the particular direction than to a displacementapplied in the particular direction.
 55. The apparatus according toclaim 54, wherein the particular direction is the Z-direction.
 56. Theapparatus according to claim 52, wherein said probe support assembly isa parallelogram flexure.
 57. The apparatus of claim 52, wherein saidprobe support assembly comprises a four bar linkage having four joints.58. The apparatus of claim 57, wherein said four bar linkage moves inresponse to movement by the actuator in the particular direction. 59.The apparatus of claim 52, wherein said probe support assembly is aflexible disc, said flexible disc being attached to said referencestructure generally around a perimeter of said flexible disc.
 60. Theapparatus of claim 59, wherein said flexible disc has a circumferentialflexure region that allows said flexible disc to move in the particulardirection.
 61. The apparatus of claim 52, wherein said probe supportassembly is a pair of flexible cross wires.
 62. The apparatus of claim52, wherein said probe support assembly moves in response to adisplacement applied thereto which is directed in the particulardirection, and generally does not move in response to displacementsapplied thereto in any direction other than the particular direction.63. The apparatus of claim 52, wherein the metrology apparatus is ascanning probe microscope.